Tempered blade



C. NAPIEH.

TEMPI-:RED BLADE. APPLICATION FILED IAN.30. 1919.

1,852,140.. Patendsept. 7, IIIzII.,

m MW im @f-La."

' of value of a still WORKS, INC., 0F SPRINGFIELD, MASSACHUSETTS, CORPORATION 0F MASSACHU- SETTS.

TEMPERED BLADE.

waaien. I original application led December 9,

Specification of Letters Patent.

Patented Sept. 7, 1920.

1918, Serial No. 265,836. Divided and this application'led January 30, 1919. Serial No. 2742,006.

To all whom z't may concern Be it known that I, CHARLES Narren, a citizen of the United States of America, and resident of Springfield, in the county of Hampden and State of Massachusetts, have invented new, and useful Improvements in Tempered Blades, of which the following is a specification.

This invention relates to comprises a blade such as other cutting implement having new and valuable characteristics. In my Letters Patent No. 1,221,576, dated April 3, 1917, I have explained a machine for uniformly temperin saw-blades, and in my Letters Patent o. 1,265,944, dated May 14, 1918, I have explained a method of heat-treating such blades adapted to be carried out with the aid of such a machine, ing a uniformly tempered blade with annealed or soft ends useful as a hack-saw and for other purposes. Such bladesare first cutting tools and hardened and then draw-tempered through' out their middles and edges to thedegree of hardness or temper 'heretofore customaryv for such blades. This customary degree of temper is such, in the instance ofthe hacksaw, band-saw and prior knowledge, as to provide a moderately iexible and resilient'blade uniformly hard enough to enable any of its edges to serve as a metal-cutting edge, the nished .blade proper, including the edge, being thus characterized by a uniform crystalline :structure with a low elastic-limit, and thereforebeing brittle a ainst sharp blows. l aware, I have collected n statistics lshowing that more than' 42 `per centum Such breakage vrepresents a loss higher vfigure if breakages ofthe tool should be inby wear.

after a partial use eluded.

A principal object of the resent inven-v tion 1s to avoid such lowes o Value by the greater hardness than a saw, knife or the productof the later patent be-` use as' to limit unduly the other such blades.. ofY

bendl or sudden the best practice 1,Ijlgwhich I am` l brittle as to require the most careful y vof hack-sawl that a cutting edge of blades are brokenA in fuse vbefore the usefulness of the cutting edge is impaired at .all

provision of a blade having ya cutting edge of has heretofore been practicable and a body which will not break under the ordinary strains of use.

Available tool-steels have heretofore vnecessitated for such uses a compromise between resilient Hexibility and hardness, a high elastic limit being attained by. drawtempering with any available material only upon treatment resulting in reducing the hardness of the metal below an attainable, and for metal-cutting purposes, the most useful value or degree. F or instance, it is my experience thata glass-hard state, attained by first heating to a high critical temperature and then chilling or quenching, is points or teeth of extreme `hardness is accompanied by such to breakage 1n brittleness and susceptibility life of the tool. It has therefore beenl customary heretofore to Isacrifice the quality of maximum hardness'inl favor of anincreased springilness and-toughness, the blades being tempered bysubjection to a moderate uniform heating after' Vhardening so as to stand lmoderate bending without breakage, despite the fact that ,this treatment'reduces the extreme hardness ofthe cutting edge which it would have; been advantageous to retain if there were any way to keep it compatible with securing toughness and resilience. When hard enoughv to cut, the blade still remains so use.

`I khave discovered ksuch a tooll asa knife, bandfsaw or hack-saw blade may be kept at a point at or near its maximum hardness, 'thereby to produce a cutting tool of heretofore unknown durability andeiiiciency, if the hard edges or p0rtlons are supported by intimate and integral contact with'portions ofl the body of the blade gradually decreasing in ,hardness and such an instrument as a metal which has been irst hardened and then drawn, as the edge is receded from, at temperatures varying with the extent of recession from the hard points or edges from about 350 to about 800 F., or such other temperature asl will leave the article in av springy resilient state. Such a spring temper is a highly desirable quality of the blade proper of such an article, but it is not comvpat'ble with sufficient hardness for metal cutting, and is as detrimental at the ultimate cutting edge or point as it is valuable in the body of the tool.

I have also devised and have explained in my application Serial No. 265,836, filed December 9, 1918, of which this is a division, a method or art of rapidly, uniformly, and if desired, continuouslyT treating such articles so as to provide them with hard cutting points or edges and with gradually and increasingly softer and more flexibly resilient supports but harder than the body ofl the blade for the point or edge and within the point or edge, and with substantially uniform spring-tempered lbodies Vintegral with and bearing such support and edge. As l an article of manufacture,`

the resulting product retains the cutting quality of hard teeth or edges against long wear, and resists breakage 'remarkably. I shall herein describe as an instance of the genus of new articles characterized by my invention a hack-saw blade, and I shall also herein describe as one instance only of the method of heat-treating such a blade also constituting a partof my invention, steps specifically applicable to this particular article,

articles comprising my invention. ,l

In the accompanying drawings,- Figure 1 is a diagram elevation of a typ' ical .specimen of the article of manufacture;

Flg. 2 is an enlarged detail of the area 2 2 of Fig. 1;

Fig. 3 is a diagram section on line 3--3 of Fig. 2 illustrating graphically the relative hardness of the metal at different parts;

Fig. 4 is a diagram plan of preferred apl paratus for practising the method;

Fig. 5 is an enlarged detail diagram in plan showing relationships of temperatures and previous conditions of the metal beingr treated; and

l, is to be expected.

f of the blade, which may be near the toothed but applicable without change except of apparatus ward the toothed edge.

Fig. 6 is a detail section at the edgeheater showing one arrangement for differentially heating the parts of the articles.

Referring now to Figs. 1, 2 and 3, if theinstrument is a saw, a preferred state vof the metal is that in which the blade 10 is substantially uniformly spring-temperedy to a flexible resilience with a highy elastic limit throughout the region 13 comprising the greater part of the body orblade; and in which the points, faces andcutting edges 15 of the teeth are of the maximum hardness compatible with enough tensile coherence to prevent chipping or shivering. At the ultimate faces, edges and points,- this may be the maximum crystalline hardness which the metal is capable of assuming, such as will follow heating above the critical temperature [1200 to'1400 F. or higher, fortool steels of commercial composition]` and immediate quenching at temperatures at or below 350 F.

If any considerable depth of the teeth or edges of the saw is in such a crystalline state, breakage under use is inevitable. For instance, if a whole tooth comprising the points and edges and faces 15 and the base or root 16 is in this state, breakage of that tooth under lateral strain or a sharp blowr or bending of the blade at a moderate angle If the region 14 adjoining the teeth is glass hard, such a breakage may involve two or more teeth. But if only the faces and edges and points are of a crystalline hardness, if the roots or bases 16 are hard but tough, and if the reg-ion 14 back of the roots 16, partakes of the qualities of resilience and flexibility, breakages of teeth do not occur. Desirably` then, the hard points and yfaces 15 and the springtempered body 13 are separated by a region 14 partaking ofthe qualities of the hard parts at these parts, and of the quality of the springy part at the juncture vat line a or cutting edge. I have found that the best results for eiiiciency and durability are attained when the region 13 is uniformly spring-temperedand when thel region 14. increases in hardness from uniformitywith the temper of region 13from the line a to- As shown graphically in Fig. 3, a'curve whose ordinates representharduess at abscissae successively approaching ,the edge rises to a maximum at the edge. r

Preferably the blade is of the "kind provided with perforations `11v at each end and with soft or annealed regions 12 at the neighborhood of the perforations, responding in this respect to the product of the art vor'method set out in my said Letters Patent No. 1,265,944. The blade proper, comprising the regions 13 between the regions 12,- 12, and the edge region 14-has first ybeen subv130 acritical temperature dependent on the material [for instance to the cherry-red hardening temperature for Y tool steels of usual carbon contents adapted to i treatment at the hardening stage.

temperature] tosudden cooling, as in an oil-bath; and the take a hardening reaction at the cherry-red has been thereaftersub]ected region 13 only has been 'tempered by'subyet-tion to a temperature in a neighborhood of .800 F., moie or less, in accordance with" the reaction of the particular metalrunder The region 14 and the faces,- edges and points 15 have been subjected to steps first hardening these regions uniformly;l then heating them vabovethe temperature for har- I dcning reaction; then chilling or quenching; and then drawing the temper of the region 14 and the bases of the teeth, points or.

edges by regulated causation of temperatures decreasing toward the edges or points and acting during a predetermined time fonly, the effect being to spring-'temper the part of the strip or region 14 at `ts juncturewith the spring-tempered blade, and to leave unaffected the condition attainedat the edges or-points when the edge containing them wasvquenclied or chilled. Preferably the quenching-of the edge strip 14 was so conducted as to occur at a regulated mlnimum temperature consonant with drawing the temper of the inner side of the strip and the inner parts of the metal blade during maintenance of thisl temperature at the chilled faces, edges and points.

These qualities of the product willbest be understood by explanation of a specific preferred instance of the steps taken in making on a commercial scale articles of the kind referred to.

Referring now to Figs. 4, 5- and 6, the process is preferably practised ,continuously by subjection of a series of the articles to bel treated successively during predetermined times to the different stages of treatment.

A convenient way to do this-to provide for4 `joining the articles end to end in a chain and lo move them forward, for instance by such means as disclosed in my saidLetters Patent No. 1,221,576, dated April 3, 1917, at a constant rate (either intermittently by short steps or continuously) past heating, quenching, reheating, tempering, cooling and washing devices suitable to the particular result desired; but it will be understood that any desired means for subjecting the articles in succession to the described stages of treatment may be employed. A preferred process is described and claimed in my said application s. No. 265,836, sied Deb. 9, 1918,

of which this application is a division. y

vThe individual yarticles 10 iirst pass through a gas-heated muflle-furnace 20 in vwhich the articles 10 and their connectors 9 are heated uniformly. Preferably the articles, if for saws, are of steel of one of the 4following typical analyses:

In either cases a temperature at muiiie 20 of from 18500 lto 14000 F. is satisfactory, and this Vis readily attained during progress Carbon steel.

Percentages.

Min. Max.A

carbon 1.05 1.10 Manganese 20 .3U Sulfur; 015 .08 Phosphorus. 015 .()9

.licon .035 .045 Nickel .003 .006

Tungsten steal.

Percentages.

Min Max .Tungsten 1.10 1.25' Manganese .20 30 Sulfur .010 08 P hosphors 010 .09 Silicon .010 .015 Carbon... 1.10 1.20 Nickel .00 003 of the saws at about 14 feet a minute through a hot passage about three feet long. From the mufHe the saws pass to a quenchlngtank -30 in which a suitable liquid, such as an oil 0r emulsion at aboutlO()O F. chills the saws to a uniform glass-hard state, eX- cept at the ends, hwhich are prevented .from rapid cooling by the mass of holders 9, and remain soft.

The saws now which to 8500, to draw the temper of the region pass yinto heater .40 in 413 to a spring-temper, and to heat the edge strip 14, 15,` again to a red heat at 140()O or more. Preferably ainetal block 41 channeled at 42 to receive all of the saw-blades except the strip 14, 15, is positioned to receive' a predetermined length of the traveling chain of saws. Heater 40 may comprise a block 41 and a refractory screen 43 supported on a base 44, and adjustable gasblasts `45 playing downward upon the eX-- posed edge strips'14 and the block 41. By proper regulation the block 41, the intensity7 temperature and number of the gas-blasts 45, no difculty is found in maintaining the relative temperaturesof the regions' 18 and I14 of thesaws at exit from the heater 4() at the desired the blades are heated to about 8000' of the length and mass of figures, which are near or slightly in excess f of 800o and' 1400o F. respectively for'the body and edge strip, as indicated' in Fig.- 4. The block 41 may be about ten inches long for an article-chain speed of 14 feet a miriute.

Saws which were cool and lglass-hardv before entering heater 40 thus leave it difl,

ferentially heated to degrees adapted to cooll slowly to a spring temperand to Achill t0 13 and stripv 14 to effect a predetermined drawing of the temper of 'the strip 14. A

' preferred treatment comprises subjecting the hot running chain of blades to the action of a stream of high flash-point oil from a nozzle 51 at a temperature near 350 F., the oil being so delivered as to cling to and follow the chain for a predetermined distance, representing a time during which there is exchange of heat by conduction between the body 13 and the bath of hot oil, and during which the heat of the body 13 and strip 14, except the edges and points, falls to or near to the temperature of this bath. The very hot strip 14, and especially the edges, faces and points 15 fall to this temperature so rapidly as to harden the cutting edges to the desired maximum degree; but the region 13 does not harden. I have discovered .that there is a sufficiently rapid drop of tem'` perature at the points and edges from red heat toward the temperature of the ,hot oil bath to carry out this reaction; that in a bath as described at or near 350 the tempering reaction at parts which have been heated only to a moderate temperature near 800 continues to the improvement of resilience and flexibility, and that a spring temper is under these conditions communicated progressively from region 13 into strip'14 to a degree depending on the time the conditions remain as indicated in bath 50. I ascribe the observed phenomena to the action in lbath 50 after the quenching of the edge 14 of the residual heat of the greater mass of metal, 'L'. e., of the body 13 of the blades, since I find the distribution of hardness in the strip 14 to depend on the distance along the running chain [and hence on the time] during which the hot stream in bath 50 is allowed to act. The depth inward from the faces, edges and points 15 'at which the metal is at maximum hardness varies inversely as this the immersion and the time taken at this stage, the shallower will be the hardest parts. The times involved are relatively short, a

eriod of about two seconds in the hot bath being sufficient for hack-saws less than El; inch thick.

The apparatus shown provides a cold bath 60 adjustable toward and away from the nozzle 51 so as to limit the time of immersion in the hot oil to produce the desired effect. Bath 60 may comprise a screen distance,so that the longer and may con- -After passing bath 60 the saws may pass.Y

through any desired forni of wash-tank containing a hot alkaline washing solution,

after which the saws are separated from the chain, and packaged for sale.

Particular attention is called to the characteristic of my new tool consisting of a region of graduated hardness greater than that of the blade or body and less than that of the cutting edges, points or faces, by the employment of which I providefor supporting the cutting edge, pomt or face on a flexible, resilient blade with a minimum liability to breakage from the blade or deformity of position with respect to the blade.

When I speak of the degree of temper or hardness of blades 4such as shown, it will be understood that I refer to a typical or average median longitudinal plane fiatwise of the blade, and that the lateral faces of any typical blade according to my invention at any part of the region 14 may be of a graduated hardness decreasing inwardly from the edge less 4rapidly than the decrease of hardness of the typical median plane within the substance of the blade. v

In some cases it will be understood that the lateral faces only of the blade at the region 14 may be at substantially maximum hardness, so long as the interior substance at the region 14 and between these faces possesses the described characteristicgraduated decrease from maximum hardness to spring temper as the edge or face of the blade is receded from.

What I claim is:

1. A blade having a hardened cutting edge and a body integral therewith and in a state of spring temper, joined by an edge region gradually varying in hardness betweenl said states, whereby the hard but brittle edge is supported against permanent bending and breakage upon a j at least as 'hard as the body of the blade, and decreasing in hardness as the edge is receded from.

2. An elongate flat blade having a hard cutting edge, an edge-region less hard, and a body tempered to a state of resiliency and not harder than any portion of said edgeregion throughout its length.

3. A cutting-tool blade having a body uniformly spring-tempered, an edge having a cutting portion of maximum hardness, and a region between edge and body varying gradually from the hardened state of the edgel to the spring temper of the body, and nowhere softer or more flexible than the body.

4. A spring-tempered saw blade charac? F. or less.

strip of metal l neaanao terized by teeth Whose edges, points and faces are in a state of maximum hardness, and by a narrow region harder and less flexible than the body of the blade lfor supporting the hard parts, said region Varying gradually from the hard state of the edge to a state of spring temper at the juncture of said region with the body of the blade.

5. A saw blade having the Cutting portions of one longitudinal toothed edge in a glass-hard state, the body of the blade back of said edge being tempered to a resilient.

flexible state, and having a region between body and edge harder and less exible than the body throughout, `Varying in temper from a springy state at its juncture With the body to glasseha'rdness near the points, faces and edges of the teeth, and adapted to support the toothed edge against breakage in use. v

6. A steelsaw blade body-portion tempered to a state of flexible resiliency7 and by teeth having points, faces and edges in a state of crystalline hardness, the metal of the teeth and of the region at the toothed edge of the blade gradually, as the edge is receded from, Varying in temper from the hardness of the faces, points and edges to the same state as the body of the blade.

Signed by me .at Springfield, Mass., this twenty-seventh day of January, 1919.

cuantas narran.

characterized by a 

